The overall objective of this program is to support a multicenter case- control study on the potential etiologic factors for sarcoidosis. Cases will also be followed to gain information on the natural history of this disease including risk factors for progression of disease. A steering committee will develop a protocol and manual of operations which will address the most promising hypotheses to be pursued to identify the cause(s) of sarcoidosis. The protocol will include a comprehensive clinical characterization of each participant and determination of markers of immune responsiveness. The contractor will participate in a system for banking biological specimens. A clinical coordinating center will be established to collect, manage and analyze the data from the clinical centers. It is estimated that the total study population will consist of 720 cases and 1,440 controls. It is estimated that each clinical center will enroll, interview, and examine 72 cases (age 21 years or older) with sarcoidosis and, enroll, interview and collect a blood specimen from 144 matched control subjects over a four year period. Clinical centers will 1) test specific hypotheses involving risk factors, familial aggregation, and genetics of the etiology of this disease and 2) describe the natural history of sarcoidosis. A six year schedule is envisioned as follows: Phase I (12 Months): A collaborative protocol and manual of operations will be developed; Phase II (48 Months): will involve the recruitment and follow-up of patients and recruitment and interviewing of control subjects, and Phase III (12 Months): will involve data analysis.